It is known that the In-containing III/V semiconductor heterostructure systems (e.g., InGaP/GaAs, InGaAs/InP) can have advantages over the Al-containing system (e.g., AlGaAs/GaAs). Among these advantages are lower susceptibility to oxidation as well as an apparent lower density of deep level states. Thus there exists a need for development of processing methods for In-containing III/V semiconductor devices.
The remainder of the discussion will be largely in terms of a particular In-containing semiconductor material, namely, InGaP. This is done for reason of conciseness and does not imply that the inventive method is thus limited.
InGaP can be selectively wet etched in HCl-based solutions, and selective dry etching of InGaP over GaAs is possible in CH.sub.4 /H.sub.2 discharges. However, not only is the etch rate of the prior art dry etching method very low (typically &lt;10 nm/min), but the method typically results in extensive hydrogen passivation in exposed III/V material, requiring annealing to re-activate dopants. Faster etch rates can be obtained with Cl-based plasmas, but at temperatures below about 150.degree. C. the resulting surface generally is rough, and typically unsuitable for further processing. Dry etching at higher temperatures may result in smoother surfaces but is not desirable because of substantial incompatibility with other process steps, and the limitation for using conventional resist masks.
In view of the potential advantages of at least some In-containing III/V semiconductor devices, it would be of considerable interest to have available a method of dry etching In-containing III/V semiconductor material that can produce smooth, substantially damage-free surfaces, can yield high etch rates substantially without incubation period, and does not require high sample temperature. This application discloses such a method.
Dry etching of metals in BCl.sub.3 -based plasmas is known. For instance, B. J. Howard et al., J. Vacuum Science and Technology, Vol. 12 (4), Part 1, p. 1259 (1994), report etching of Cu in BCl.sub.3 /N.sub.2 as well as in BCl.sub.3 /Ar. At 225.degree.-275.degree. C. the Cu etch rate in the former plasma was found to be as much as an order of magnitude larger than in the latter. They report that N.sub.2 does not merely act as a diluent but rather increases the concentration of Cl atoms.
By way of further examples, W. F. Marx et al., J. Vacuum Science and Technology, Vol. 10 (4), Part 1, p. 1232 (1992), report electron cyclotron resonance (ECR) etching of Al alloys with BCl.sub.3 /Cl.sub.2 /N.sub.2. Japanese patent application Publication No. 06-069236, Mar. 11, 1994 reports etching of an Al/Ti/amorphous Si film in a BCl.sub.3 /Cl.sub.2 /N.sub.2 plasma, and Japanese patent application Publication No. 05-251401, Sep. 28, 1993 reports etching TiW in a BCl.sub.3 /SF.sub.6 /N.sub.2 plasma. Japanese patent application Publication No. 02-084721, Mar. 26, 1990 discloses forming a trench in Si by dry etching with BCl.sub.3 and N.sub.2 at 10 mTorr and -250 V, and Japanese patent application Publication No. 63-136526, Jun. 8, 1988 discloses forming a tapered via hole through a GaAs body by reactive ion etching in BCl.sub.3 /Cl.sub.2 /N.sub.2 at 1.7 Pa, with N.sub.2 addition resulting in reversal of the taper of the via hole.